DESCRIPTION:(Adapted from Applicant's Abstract) This is a revised application previously reviewed by the November Study Section. Previous experiments form this laboratory have provided evidence that binding of a triple helix forming oligonucleotide (TFO) to clustered Sp1 sites in the viral LTR could repress transcription of HIV-1 in a chronically infected monocyte cell line. The overall goal of this proposal is to develop a program of rational drug design to improve TFO binding by employing advanced molecular modelling techniques, NMR and recent advances in nucleic acids chemistry. The specific aims of the proposal are: (1) Refine the general understanding of triplex structure, especially the role of water and ion binding, employing molecular modeling and 2DNMR methods. (2) Use modeling, NMR and related physical methods to evaluate the utility of imidazole-nucleoside homologues in TFOs. (3) Design major groove binding agents which may be affixed to the ends of TFOs so as to enhance the stability of the bound complex. (4) Synthesize HIV33-class TFOs which contain such base substituents and stabilizing end modifications and evaluate their structure, stability and selectivity of binding to the LTR. (5) Exploit the apparently large change of helix twist which may accompany RRY triple helix formation using a "phasing" plasmid assay. This assay will explore the twist change which may occur upon TFO binding to the HIV-1 promoter region and will also explore effect of polymeric linker elements which are synthesized into the center of the TFO. (6) Employ lipophilic 3'- end modification of the cholesterol type and novel cationic lipids to enhance the cellular uptake and intracellular partitioning of TFOs of the HIV 33 class. (7) Measure anti-HIV activity in acutely and chronically infected cells of modified TFOs of the HIV 33 class which display enhanced LTR binding, enhanced uptake, or torsional distortion of the binding site.